Silicon photonics can allow for high density component integration on a single chip and it can bring promise for low-loss, high-bandwidth data processing in modern computing systems. The technology, when combined with wavelength division multiplexing (WDM) systems, can portend a future generation of 100+ Gbit/s networks, particularly in terms of making them more cost effective than 10 Gbit/s and 40 Gbit/s nets. WDM can enable multiple channel data transmission in a single fiber-optic link and can dramatically increase the aggregate data rate.
Optical waveguides are known in the prior art for use in these photonics applications. Often times, optical waveguides can have a protective cladding. This can be particularly true when extremely small waveguides are patterned on silicon chips. For efficient light transmission through the waveguide, it can be desirable to maximize light confinement within the waveguide during transmission. To maximize light confinement, it can be desirable for the difference between the cladding refractive index and the waveguide refractive index to be as great as possible. Thus, it can be desirable to have an optical film, or cladding material (in the specification, cladding can be taken to mean the act or process of bonding one film or substrate to another, or to mean the film or substrate used to accomplish the bonding process, but where the film materials are not necessarily metallic) with as low a refractive index as possible. Currently there are very few optical thin films that possess low refractive indices, and optical materials with indices between about n=1.1 to about n=1.20 do not exist.
Silicon dioxide (SiO2) is a commonly used material with applications in photonics and microelectronics. It can be used in optical fibers due to its low absorption of light and by virtue of its excellent electrical insulation properties, and it can function to protect silicon, block current and store charge in electrical applications. In silicon photonics, SiO2 is typically used as the cladding material surrounding a silicon waveguide core. Typical methods of SiO2 deposition can include chemical vapor deposition (CVD) processes such as low pressure (LPCVD), plasma enhanced (PECVD), microwave plasma (MPCVD), or thermal oxidation. One of the key advantages of silicon photonics lies in leveraging standard CMOS manufacturing equipment and using these typical CVD processes to enable high volume production, in addition to the feasibility of monolithically integrating most of the electronic-photonic components on a single chip. This can significantly reduce assembly processes, which can drastically reduce component sizes.
Of the CVD methods mentioned above, PECVD systems have entrenched their place in the electronics sector because of their flexibility in depositing many thin films such as silicon nitride (Si3N4), silicon monoxide (SiO), silicon dioxide (SiO2), silicon oxinitride (SiON), diamond-like carbon (DLC), amorphous-silicon (a-Si) and polycrystalline-silicon (poly-Si) for integrated circuit applications. Also, the PECVD process can be accomplished at much lower temperatures than other CVD processes. However, the PECVD process can lead to less dense films, and PECVD oxides produced at lower temperatures can be significantly more porous than those deposited at higher temperatures. For silicon photonic applications, these PECD “disadvantages”, combined with less than optimal step coverage and inhomogeneous coverage of 3D nanostructures, can result in areas of lower density SiO2 in the vicinity of silicon strip waveguides. In the past, this effect has been viewed as sub-optimal and consequently this material non-uniformity has been overlooked thus far in the Si nanophotonics community. If a “uniform non-uniformity” resulting from the more convenient PECVD processes could be achieved, at least in the areas in contact with and immediately adjacent the waveguide, an extremely low refractive index film can be accomplished.
Such extremely low refractive index materials could find use in distributed Bragg reflectors, which are periodic structures that can consist of an alternating series of a quarter-wavelength thick high-index and low index material with a refractive index of nhigh and nlow. Low index materials could also find use in other periodic structures, such as photonic crystals, plasmonic arrays or metamaterials, as well as in microelectronic applications for electrical isolation as a gate oxide, sidewall spacer or field oxide. They may also be useful as an etch stop or sacrificial layer in micro-mechanical fabrication. Still further, the materials could also be used in light emitting devices for electrical isolation or graded index (GRIN) antireflective coatings, as the figure of merit of these structures depends on the refractive index contrast (or difference) between the layers. Low index claddings could be used for optical fibers and other optical waveguides (i.e. chip scale). Currently, silicon dioxide (n=1.46) and magnesium fluoride (n=1.39) are commonly used. Other potential application areas can consist of filters, band-passes, lasers, LEDs, and solar cells.
In view of the above, it can be an object of the present invention to provide an optical waveguide and method of manufacture in accordance with several embodiments that can achieve better light confinement within the waveguide. Another object of the present invention can be to provide an optical waveguide and method of manufacture with a cladding having a greatly reduced refractive index. Still another object of the present invention can be to provide an optical waveguide and a method of manufacture that can be manufactured at a reduced temperature using a PECVD process. Yet another object of the present invention can be to provide an optical waveguide and method of manufacture that can have an increased difference between the waveguide and cladding material refractive indices. Still another object of the present invention can be to provide an optical waveguide that can be manufactured and deployed in a relatively efficient, cost-effective manner.